Embattled D.C. Council Chairman Kwame R. Brown solidified his grip on the 13-member body Tuesday, booting a nemesis from his committee chairmanship while greatly expanding the influence of one of his chief allies and confidants, council member Mary M. Cheh.

In a highly unusual midyear reshuffling of committee assignments, Brown (D) unnerved progressives and members of the business community when he removed council member Tommy Wells (D-Ward 6) as chairman of the Committee on Public Works and Transportation after a 12 to 1 vote. Brown also replaced Wells, the council’s chief advocate for smart-growth policies, as the District’s representative onMetro’s Board of Directors.

Brown opted to keep two of the council’s most essential functions — oversight of public schools and economic development — under the purview of a committee he chairs.

“It’s a little unsettling, because it’s a lot of change,” said Barbara Lang, president and chief executive of the D.C. Chamber of Commerce. “Businesspeople like stability, and we like things to stay put.”

Brown announced the changes during the final council session before the body takes a two-month recess. The council rejected a proposal that would have made the city government a federal firearms dealer so residents could more easily transfer handguns bought in other states into the District. Members also agreed to cap the pay of Police Chief Cathy L. Lanier and Schools Chancellor Kaya Henderson and approved a bill that delays the collection of a new tax on municipal bonds until Jan. 1.

But the meeting was largely consumed by Brown’s decision to shake up members’ committee assignments. The changes come as Brown tries to make friends and boost his influence while battling several ethics controversies, including his request for a taxpayer-funded sport-utility vehicle and allegations that he failed to disclose more than $270,000 in campaign donations and expenditures for his 2008 reelection campaign. The U.S. attorney’s office is investigating.

As Brown tries to jump-start his agenda while fending off what he views as unfair media attacks on his character, he appears to be working to guarantee that he can count on a veto-proof majority.

“He needed some realignment to get things done,” said Marion Barry (D-Ward 8), a Brown ally.

Brown, who was sworn in as chairman in January, said he had long planned to make some changes to committee assignments to make the council run more efficiently. “You have to make decisions and choices, and everyone is not going to be absolutely happy, but at the end of the day, residents are going to get the best outcome,” Brown said.

But some advocates and council members think Brown was out to punish Wells, who led the council investigation into his request for the SUV and outmaneuvered the chairman during a debate last month on the fiscal 2012 budget.

“I’m consistent on ethics and good government,” said Wells, who will be chairman of the Libraries, Parks and Recreation Committee. “That may make some of my colleagues uncomfortable.”

As part of the shake-up, Brown created a committee that combines responsibility for environmental, transportation and public works issues.

Brown named Cheh, a Democrat who campaigned extensively for him in her home base of Ward 3 last year, as the next chairman of that committee.

He said that the new committee will consolidate the council’s efforts to address issues such as stormwater runoff, an expansion of public transportation and waste management.

Brown said Cheh is a good fit to head the committee because she has a long-standing interest in environmental issues. But Brown’s decision highlights how quickly Cheh’s power has increased under his leadership.

In January, Brown named Cheh, who was first elected in 2006, president pro tempore of the body, removing five-term council member Jack Evans (D-Ward 2) from the high-profile position often reserved for the most senior member. Three months ago, Brown tapped Cheh’s former chief of staff, Dave Zvenyach, as the council’s general counsel.

In an interview, Cheh said Brown is giving her new opportunities because she has a “very strong record on the council as someone who gets stuff done.”

“I think people have confidence in me,” said Cheh, adding that she hopes to work closely with Wells, whom she says she agrees with on “99.9 percent” of issues.

But in a sign of Cheh’s close relationship with Brown, the chairman also initially spoke with her about taking over from Wells as council representative on the Metro board.

Instead, Brown appointed Muriel Bowser (D-Ward 4) to the post, which adds more unpredictability to a body in which three-fourths of the members have been on the job less than a year.

Wells, whom Brown had appointed to the WMATA board in January, said the abrupt change was “reckless” and “undermines the seriousness” of the District’s commitment to improving Metro service. But Brown noted that Bowser already chairs the Metropolitan Washington Council of Governments’ transportation planning board.

Bowser, a longtime ally of former mayor Adrian M. Fenty’s (D), is often a swing vote on the council. Another potential swing vote, Vincent B. Orange (D-At Large), was also tapped to head a new committee Tuesday.

Last month, Harry Thomas Jr. (D-Ward 5) was forced to step down as chairman of the Economic Development Committee over allegations that he diverted public funds to a nonprofit group he controlled. Brown said that Orange will head up the new Committee on Small and Local Business Development.

But Brown is retaining oversight of the deputy mayor of planning and economic development on the Committee of the Whole, which all members sit on but he chairs.

The decision ensures that he will have broad influence over efforts to lure companies to the District.

Bowser will also become chairman of the Government Operations Committee, which had been led by Cheh.

Staff writer Mike DeBonis contributed to this report.